EP1551290B1 - Impedance-based measuring method for hemodynamic parameters - Google Patents

Abstract

The invention relates to a method for measuring the volume, the composition and the movement (HZV) of electroconductive body fluids, based on the electrical impedance of the body or a body segment, especially for performing electromechanocardiography (ELMEC) or impedance cardiography (IKG) measurements for determining hemodynamic parameters. According to said method, an alternating measuring current (52) of at least one frequency is introduced into the body (60, 70), and the impedance and temporal variations (AZ) thereof of essentially the same body segment through which the alternating measuring current flows are measured for at least two different measuring lengths (L, L2, L3, L4, L5), essentially in the longitudinal direction of the body.

Description

The invention relates to a method for measuring the volume, the composition and the movement of electrically conductive body fluids, based on the electrical impedance of the body or a body segment, in particular for the electromechanocardiography (ELMEC) or impedance cardiography (ICG) measurement for determination haemodynamic parameter, wherein an alternating measuring current of at least one frequency is introduced into the body by measuring electrodes applied to the body surface.

In medicine, there is often a need to measure the mechanical action of the heart. Thus, the impact force, the inotropy, the contractility and the ejection fraction (Ejection Fraction) are measured by various methods, such as echocardiography, with or without color Doppler. Furthermore, the amount of blood ejected from the heart within a heartbeat, the stroke volume and other hemodynamic parameters is often determined. If the heart rate is known, this can be used to calculate the cardiac output (CO = cardiac output = cardiac output = CO). From the mentioned variables, the function of the heart can be deduced and the diagnosis of cardiac diseases can be made or new physiological findings can be obtained. However, monitoring of severely cardiac patients in intensive care units or during anesthesia by means of echocardiography can not really be done because there should always be an examiner present. Because of the importance of this problem, there are also many other methods of measuring CO in the medical field. Thus, for example, a catheter is introduced into the pulmonary artery and / or into the aorta and there is by means of an indicator size or substance, which may be, for example, heat, cold, common salt or lithium, within a measuring section of the waste measured the concentration of the mentioned indicator substance and then measured by means of Fick's principle, the CO. The disadvantage of this method is the introduction of a catheter into a human vessel with all the resulting complications, such as bleeding and infection. It is therefore an invasive procedure that involves high costs because of disposable catheters and high risks to the patient [ ⁱ , ⁱⁱ ]. In addition, the principle of thermodilution or dye dilution has a wide range of errors, so that usually the average of several measurements is used to obtain a plausible value. Under physical stress, or in other states where the body temperature changes, the thermodilution delivers wrong values.

Recently, attempts have been made to apply the Fick's principle for the measurement of cardiac output by measuring gases in the breathing air. This is possible because there is a very rapid gas exchange between blood and respiratory air, so that one can virtually equate the concentrations in these two media. If a gas is added to the respiratory air, its concentration also increases in the blood, stops the burial of the gas, then there is a drop in the gas in the blood and in the air, in turn, from the drop in concentration in the unit of time according to Fick's principle, the CO can be measured. One method that has proven to be particularly useful is CO ₂ rebreathing. A loop is introduced into the respiratory tract of the patient and the patient breathes his own exhaled air for a certain period of time, resulting in an increase in the CO ₂ concentration in the blood. The disadvantage of these methods is that the patient must be provided with a mouthpiece and as constant breathing as possible, so that a uniform concentration of the respiratory gases in the breathing air and in the blood is ensured. Therefore, this procedure is mainly used in anesthesia with constant tidal volume and constant respiratory rate. In spontaneously breathing patients, the disadvantage of breathing through a tube system with mouthpiece is maintained, which increases the dead space of breathing considerably and also the respiratory resistance and thus the Exhaustion of breathing increased. In addition, the accuracy of the method in spontaneous breathing decreases sharply. Another method consists of a similar method whereby, instead of CO _2, an inert gas which is inhaled and which also rapidly equilibrates with the blood is used for the measurement of CO.

Another method is the measurement of stroke volume and other hemodynamic parameters from the pulse shape taken at a peripheral artery. A change in the pulse shape is also caused by a change in the stroke volume and other hemodynamic parameters, from which indirectly the change in stroke volume and other hemodynamic parameters can be derived via a transfer function. This method must be calibrated in the beginning with one of the methods described above, and it is also not sufficiently accurate. Another known method is to measure an indicator substance, e.g. Indigo green transcutaneously on the capillaries of the ear or fingers, which greatly reduces the accuracy of Fick's principle.

Another method known from the prior art is impedance cardiography IKG. In this, a constant AC field is applied to the thorax, and the change in AC voltage produced by this AC field indicates a change in the fluid content in the thorax. More specifically, the AC resistance (impedance) is measured by this method, which is a measure of the change in thoracic fluid content. This change in fluid content in the thorax, in turn, serves as a measure of the amount of blood ejected per beat. From the stroke volume and other haemodynamic parameters (SV) and the heart rate (HR), the cardiac output (HRV = SV * HR) can then be calculated.

Usually, a pair of electrodes leading the current to the body is placed above or at the top and bottom or at the bottom of the thorax. Within this pair of electrodes, a second electrode pair for measuring the resulting AC voltage attached. In this pair of internal electrodes, the correct mutual distance must be maintained, namely that the upper voltage electrode must be at least at the level of the glottis and the lower electrode at the level of the xiphoid. The distance between the two electrodes is thus dependent on the length of the thorax and is described as the electrode measuring length L in the further sequence. The impedance Z (t) = u (t) / l _{0 is} calculated, where u (t) is the alternating voltage which changes and l _{0 is} the constant-current alternating current injected into the body.

So far, either circular electrodes or point electrodes, similar to ECG electrodes, have been used for this purpose. In the patent application "Medical Electrode" [ ⁱⁱⁱ ] a new electrode arrangement has been described, in which two band electrodes are mounted in parallel on the same film over a short distance, their spacing being precisely predetermined and reproducible by the common carrier foil. One of these parallel strip electrodes, which is applied to this common carrier film, serves to apply the measuring current, the other parallel band electrode is provided for the derivation of the measuring voltage. The upper pair of electrodes (or double electrode) can be attached to the neck, for example, and the lower pairs of electrodes to the left and right of the lower thorax aperture. This electrode arrangement shows a significantly better reproducibility of the results than the ring electrodes used earlier or better than those in the patent application US 4,450,527 S _RAMEK [ ^iv ] (Fig. 1a + 1b ) Spotelektroden described.

Disadvantages of the described impedance methods so far have been that the results were calculated either according to the KUBICEK equation [ ^v , ^vi ] or according to the SRAMEK equation [ ⁴ , ^vii , ^viii ], both of which were derived with very simplistic assumptions about the human body , These assumptions are only partially true, so there is also a considerable error in the calculation of stroke volume and other hemodynamic parameters and cardiac output.

Equation 1 shows the KUBICEK equation for calculating the stroke volume and other hemodynamic parameters from the change in the impedance signal: $$\mathit{SV}=\rho *\frac{L^2}{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0^2}\cdot \mathit{LVET}\cdot (\mathit{dZ}\mathit{/}\mathit{dt}{)}_{\mathrm{Max}}$$

Where L is the measured length between two electrodes measured in [cm] at the surface of the body, where p is the specific resistance of the blood in [Ωcm], where Z _{0 is} the basic impedance in [Ω], with (dZ / dt) _{max is} the maximum height 1. Derivation of the electrical resistance or impedance change after time in [Ω / sec] by the heart action and with LVET, the left ventricular expulsion time [sec].

oder aus einer ähnlichen Formel geschätzt bzw. auch in anderen Verfahren einfach konstant gehalten. Dabei bleibt unberücksichtigt, dass es nicht nur der Hämatokrit ist, der die Leitfähigkeit des Blutes verändert, sondern auch die Ionenkonzentration im Plasma sowie die darin befindlichen Eiweißstoffe. Deswegen wird aus einer empirisch gewonnenen Gleichung, die nur einen und nicht alle Blutbestandteile berücksichtigt, nie die genaue Leitfähigkeit oder der Widerstand des Blutes zu ermitteln sein. Weiters ändert sich auch die Leitfähigkeit des Blutes durch die Flußgeschwindigkeit, da bei größeren Geschwindigkeiten die Erythrocyten sich im Blutstrom längs ausrichten und damit den Flüssigkeitsquerschnitt vergrößern. Bei noch höheren Geschwindigkeiten und daraus entstehenden Turbulenzen kann der Widerstand des Blutes wieder ansteigen.As can be seen, in this equation, on the one hand, the electrode measuring length L is square, whereby this electrode measuring length is currently measured at the thorax surface. Furthermore, the specific resistance p of the blood is linearly introduced into the formula, wherein the specific resistance of the blood depends primarily on the blood content of red blood cells. According to the law of LAMBERTS ET. AL. [ ^ix ] p is approximately calculated from the hematocrit Hkt by means of the formula $$\mathrm{\rho }\mathrm{=}\mathrm{71}\mathrm{.}\mathrm{24th}{\mathrm{e}}^{\mathrm{0}\mathrm{.}\mathrm{000358}\mathrm{Be\; up}\mathrm{2}}$$

or estimated from a similar formula or simply kept constant in other methods. It is not taken into account that it is not only the hematocrit that changes the conductivity of the blood, but also the ion concentration in the plasma and the proteins contained therein. Therefore, an empirically derived equation that takes into account only one and not all of the blood components will never determine the exact conductivity or resistance of the blood. Furthermore, the conductivity of the blood changes by the flow rate, since at higher speeds, the erythrocytes align themselves longitudinally in the bloodstream and thus increase the liquid cross section. At even higher speeds and resulting turbulence, the resistance of the blood can rise again.

In the formula according to SRAMEK, 17% of the body height is entered instead of the electrode measurement length, because empirically it has been found that the thorax length accounts for about 17% of the total body length. Another assumption in this formula is divisor 4.25, which is derived from the estimated relationship between electrode gauge length and waist circumference, as well as an estimated constant ratio between a cylindrical thorax model and a frusto-conical thoracic model ( US 4,450,527 , Column 5, line 50 ff.). Thus, the length of the body H is even cubic in the formula. $$\mathit{SV}=\frac{{\left(\mathrm{12:17}\cdot \mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">H</figure-callout>}\right)}^2}{4.25}\cdot \mathit{LVET}\cdot \frac{(\mathit{dZ}\mathit{/}\mathit{dt}{)}_{\mathrm{Max}}}{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0}$$

wobei es sich bei β um einen "Blood volume index" handelt, und W _ideal und W _real um das Idealgewicht und Realgewicht eines Menschen handelt.Bernstein [*] further "corrected" this formula by multiplying the above formula by a correction factor δ. $$\mathrm{\delta }\mathrm{=}\mathrm{\beta }\left({\mathrm{W}}_{\mathrm{real}}\mathrm{/}{\mathrm{W}}_{\mathrm{ideal}}\right)$$

where β is a "blood volume index" and W is _ideal and W is the ideal weight and _real weight of a human being.

The ideal weight in men is: $$\mathrm{W\; ideal}\mathrm{=}\mathrm{0}\mathrm{.}\mathrm{534}\mathrm{H}\mathrm{-}\mathrm{17}\mathrm{.}\mathrm{36}$$

The ideal weight for women is: $$\mathrm{W\; ideal}\mathrm{=}\mathrm{0}\mathrm{.}\mathrm{534}\mathrm{H}\mathrm{-}\mathrm{27}\mathrm{.}\mathrm{36}$$

H denotes the size of humans in [cm].

It can be seen that in all equations different units of measure are mixed together. Thus, the equations obtained have nothing to do with truly derived, credible mathematics. By incorporating anthropometric variables into the equation, an indirect measure of the stroke volume and other haemodynamic parameters of the heart in the healthy is also directly included in the calculation of stroke volume and other hemodynamic parameters. The HZV namely fits the healthy to the body surface like a tailored suit. Thus, a parameter enters the formula that has nothing to do with the measurement of stroke volume and other hemodynamic parameters, namely the body measurements of the patient. Therefore, a large patient automatically has a larger stroke volume and other, larger hemodynamic parameters than a small patient by introducing the body size or body size dependent electrode length L between the glottis and xiphoid into the calculation formula. Also in the formula of Kubicek mentioned above, a measure of the dimensions of the body goes directly into the formula.

As in Fig.1 The measuring length between the electrodes, when properly applied to the upper and lower thorax apertures, is surprisingly well correlated with the size of the patient.

In the case of healthy heart, the agreement of bloody measured stroke volume and other haemodynamic parameters with the impedance cardiography according to the above explanations is good because actually the height of the body is a measure of the cardiac output. A large, heavy human, in fact, has to carry much more blood to the tissues in the unit of time than a small, delicately-built human being. In cardiac patients, this principle is no longer upright, therefore, the correlation between the actual cardiac output and the cardiac output measured by impedance cardiography is very poor or non-existent, because suddenly the body masses no longer introduced into the formula Meaning. It therefore arises in cardiac patients, an enormous bias toward normal and thus falsely high values.

In addition, the value determined by means of impedance cardiography is additionally falsified in the wrong direction by the following phenomenon, namely in those too high CO values. In patients with heart failure, the majority of the body's water in the chest is due to the disease, rather than heart. This increased thoracic fluid content naturally reduces the basic impedance Z ₀ in Ω. This value is inverted (SRAMEK) or square inverted (KUBICEK) into the respective calculation formulas and falsifies the calculated value of the CO, which can lead to fatal misdiagnosis. In heart healthy Z _{0 is} a measure of the thorax geometry, in heart failure patients with increased thoracic fluid content, this is just not the case.

This will be in Fig. 2 clearly demonstrated. Here, the ejection fraction (Ejection Fraction EF) was measured echocardiographically in patients with and without heart failure using the Simpson method and the ejection fraction compared with the CO. The echocardiographic parameter EF was therefore chosen instead of the echocardiography measured CO, because it is much more precise to measure. As can be seen, there is no correlation between CO and ejection fraction, which would be expected in and of itself if impedance cardiography had significance in cardiac insufficiency.

Because of this, cardiologists have found that impedance cardiography is not really successful, at least in Europe, because it may be good for healthy individuals to match the actual stroke volume and other hemodynamic parameters, but the accuracy is high in heart patients, where the value is really diagnostic bad. Nevertheless, in America, the method is now increasingly used because it has been shown that the relative changes in stroke volume and other hemodynamic parameters can be tracked well, so that the effect of pharmacological interventions can be well tracked even if the absolute values are wrong.

None of the devices on the market would also be able to output a value of the stroke volume and other hemodynamic parameters or cardiac output unless at least the body size, or the thorax length between the electrodes, that is another measure of body size, is entered. Especially in intensive care units, there is often no way to measure or ask for weight and size. If an incorrect value is entered, which can easily happen in practice, the result would be additionally further falsified.

However, a device or method for determining the cardiac output should also provide a reliable value if no a priori knowledge of height and weight is available, as is of course also the gold standard of thermodilution, or in other methods that the fuck 'use specific principle as the method of CO ₂ rebreathing is possible or other breathing gas methods. As soon as a priori knowledge of the body measurements is used, the measurement result is already influenced in the direction in which the measured value of the cardiac output should go, that is, bias is introduced into the equation, which falsely good results of the heart healthy people Method pretends. In addition, with an electrically measured cardiac output , only electrically measured parameters should find room in the equation.

When in the US 4 450 527 A described impedance measurement device, the dimensions of the thorax, in particular the measuring length between the electrodes, where measured, be determined and entered. The chest impedance is measured as a function of time and the effects caused by the respiratory motion are eliminated so that a normal breathing of the patient is made possible during the measurement process. spot Electrodes for current injection on the one hand and for picking up a measuring voltage are applied in the neck area and in the sternum area. The measuring length between the lower and the upper electrodes is not changed during the measurement.

In the US Pat. No. 5,109,870 A For example, a catheter for measuring motility and peristalsis in tubular organs, eg, the esophagus, is shown by simultaneous, multiple impedance measurements that include an isolation plastic tube, annular electrodes, and internal channels for the electrode leads. The annular electrodes are connected to impedance transformers, which convert the measured signals into voltage and current signals so as to be able to display them. Because of this multiple electrode arrangement, a simultaneous measurement of a multiplicity of measurement channels can be carried out in order to obtain conclusions about the movement and transport characteristics of the organ. For this purpose, the catheter must be inserted into the organ and fixed in this in a certain position. Even for a patient who is in a stable state of health, this measurement method is very stressful and therefore can not be repeated as often as desired. The cardiac output is not determined by the given method.

Furthermore, in the US 4 951 682 A a cardiac catheter is provided for measuring cardiac output with a plurality of spaced-apart ring electrodes. In the introduction (column 2, second paragraph) of this document, non-invasive methods for determining the cardiac output are discussed and found that all of them have serious disadvantages and the invasive measurement by means of cardiac catheter would have decisive advantages. Reference is made to invasive cardiac catheterization alone, which by its nature is not very often performed on a patient and can result in significant complications.

From the US 4,947,862 A goes out a device for determining the body fat percentage of a patient, in which a high-frequency current is introduced into the body and a voltage is tapped. Amplitude and phase detection circuits measure the amplitude and phase of the generated voltage signals versus impressed current. Body size, weight and age must be determined and entered into an input device, whereby measurement errors of these values are included in the calculation of body fat percentage.

Finally, in the US 5 063 937 A a multiple-frequency measurement system for determining the bio-impedance of a patient's body over a wide frequency range specified, with errors in the determination of the measuring length between the electrodes are not taken into account.

The object of the invention is therefore to provide a method of the type mentioned above, in particular for determining the stroke volume or in general also for the measurement of other hemodynamic parameters such as inotropy, ejection fraction, by means of impedance cardiography, which helps to avoid the aforementioned disadvantages.

According to the invention this is achieved the features of claim 1.

By measuring the impedance or changing it at two different measurement lengths, the actually electrically participating "operative body segment length" or the actually participating electrical "operative body segment volume" or the actually measured "operative specific resistance" of the blood can be integrated with solutions of equations Electrically determine several unknowns or with empirically derived equations this introduce additional information in a so-called "black box" model, in which only more electrically measured quantities are received. The dependence on body dimensions and other body measurements is eliminated.

Since, in particular in the determination of the cardiac output, the impedance changes in the thoracic region have a significant significance and it has proven to be favorable to make the change in the electrode measuring length in the main flow direction of the blood, it can be provided in a development of the invention that the impedance at the thorax close to the chest upper and lower thorax aperture at at least two different measuring lengths of the substantially same body segment is tapped.

Another variant of the invention, in which the impedance is tapped on the trunk near the upper and lower end of the fuselage at at least two different measuring lengths of the substantially same body segment, has the advantage that the impedance of the extremities can also be measured at two different distances so that an operative length or an electrically participating volume can also be determined for this area.

When the measuring current in the thorax or trunk area is introduced, current bellies result in the interior of the body, while the measurement is as straightforward as possible Stream spreading is advantageous, as it can be achieved by current injection through the body ends. A further variant of the invention can therefore be that the current is introduced at or near the lower end of the body instead of at the lower thoracic aperture and the impedance at the thorax and / or the trunk and / or the extremities is measured in each case at at least two different measurement lengths ,

For the determination of some haemodynamic parameters or parameters for the fluid balance, it may further be advantageous if, in addition, the whole-body impedance, ie the impedance between the lower and upper body end, is measured. This additional measurement of whole-body impedance can be applied not only to the inventive method but also to any other conventional method of impedance cardiography measurement, it is claimed for this independent of the measuring method according to the invention with different electrode gauge length protection, including for those already from the state of Technique known generic processes.

The greatest possible accuracy and reproducibility of the impedance measurement is furthermore provided if the difference in length between the two different measurement lengths is small in relation to the length of the measured body part, in particular if the ratio of the length of the examined body part to the difference between 3: 1 and 50: 1, in most preferably about 10: 1.

In the impedance measurement on the body, an alternating measuring current can be impressed via current electrodes which are spaced apart from one another on the body surface by a current electrode measuring length and via voltage electrodes which are impressed on the body surface, in particular on the thorax surface, by a voltage electrode measuring length are spaced apart, a measuring voltage caused by the measuring current are tapped, and from the measuring current and the measuring voltage, the electrical impedance or its temporal change are calculated.

An embodiment of the invention may consist in calculating an operative electrode measuring length or optionally additionally an operative electrode distance from the impedance values determined between electrodes at different measuring lengths. By means of these actual values which are effective in the body, a reliable determination of the impedance or its change can be achieved. In this way, it is possible to dispense with the manual measurement of the changes in the electrode measuring length.

Thus, the electrically operative length of the body segment can be calculated from the formula L ₀ = d / (Z ₀₂ / Z ₀₁ - 1), where d is the length difference between the two electrode measuring lengths used for the measurement, with Z ₀₂ the impedance the longer electrode measuring length and with Z ₀₁ the impedance over the shorter electrode measuring length is designated.

In order to avoid an asymmetrical current distribution in the body of the patient, it can be provided according to another embodiment, that the voltage electrodes on the lower thorax aperture are designed as double electrodes on the left and right sides of the thorax, wherein the electrodes lying in the longitudinal direction on the same longitudinal distance electrically connected to each other.

Alternatively, it can be provided that either the left and right electrodes lying on the thorax aperture can be switched off.

When attaching measuring electrodes to the fuselage, an advantageous embodiment of the method according to the invention can consist in that the voltage electrodes at the lower end of the fuselage are designed as double electrodes on the left and right at the lower end of the fuselage, whereby in each case the electrodes lying in the longitudinal direction on the same longitudinal distance electrically connected to each other. Thus a relatively large body volume can be detected by the measurement become. Alternatively, alternatively, the left and right respectively at the lower end of the fuselage lying electrodes can be switched off.

By attaching at least one additional current electrode and / or voltage electrode results in a modified Elektrodenmesslänge the current electrodes and / or voltage electrodes with respect to another electrode element, preferably in the longitudinal direction of the body, and thus in the main flow direction of the blood, so that simultaneously or alternately the measurement the impedance and its change in the thorax can be done in each case with the shorter and longer electrode measuring length. This change in the electrode gauge length L should be constant, known, or calculable.

However, the objects of the invention in a method of the aforementioned type can also be achieved by measuring the electrical impedance at two or more measuring frequencies and determining the fractions of the intracellular and extracellular spaces, and these quantities for calculating the stroke volume and others haemodynamic parameters are used. This method can be applied independently of the defined change in the measuring length according to the invention, also in an ordinary two-electrode system or else in combination with it. By choosing the two measurement frequencies, the property of the blood to assume a different resistance at different frequencies can be used to determine various hemodynamic parameters for which the specific resistance of the blood is important.

The number of different frequencies that are used for the inventive method is unlimited upwards, also a continuous sweeping of a frequency band (sweep), preferably from a lower measurement frequency up to an upper measurement frequency, is within the scope of the invention, the lower Measuring frequency according to a preferred embodiment of the invention is about 1 kHz and the upper measuring frequency is a maximum of about 1000 kHz.

The phase angle between the measuring current and the measuring voltage at different frequencies can also be a measure for the determination of haemodynamic parameters.

An advantageous embodiment of the method according to the invention can consist in the fact that the electrical impedance or the impedance characteristic is measured simultaneously over time at two measuring frequencies. The two frequencies can be e.g. be separated by frequency filters (frequency multiplexer). Alternatively, one and the other measuring frequency can be measured alternately in very short time windows. From the different impedance values that can be measured at different frequencies, the body water distribution can be determined and inferred to the thorax geometry.

A further embodiment of the method according to the invention may be that the impedance is measured at three different frequencies, the different frequencies being between 1 and 10 kHz, 30 to 100 kHz and higher than 200 kHz.

As already explained, one of the problems of impedance cardigraphy is the determination of specific blood resistance, which plays a role in various calculation formulas of haemodynamic parameters. Since the decrease of the maximum time derivative of the impedance after the time with increasing frequencies is a measure of the specific resistance of the blood, the objects of the invention can be solved in a method mentioned above by determining the maximum temporal change of the measured impedance values (dz / dt) determined at at least two different measurement frequencies and from these the specific resistance of the blood in the body is determined. Such a measurement may be performed with or without changing the gauge length between the voltage or current electrodes.

From the impedance changes e.g. at a high and at a low measurement frequency, a ratio can be calculated which is a measure of the erythrocytes deformed by the acceleration in the aorta. From this ratio, further parameters can be derived by suitable mathematical signal analysis, which are significant for the calculation of the heartbeat volume.

Thus, according to a development of the invention, the maximum temporal change of the measured impedance value, in particular in relatively narrow time windows, at different times of the heart period, can be determined. In this way, a temporal averaging of the impedance value changes over the heart period results.

Averaging from the extreme values of a heart period can be carried out according to a further variant of the invention in that the time windows are set at a steep increase in the specific resistance and at the time of the minimum blood flow at the end of the diastole.

If time windows are laid as narrow sliding windows over the entire cardiac period, then the accuracy of the method according to the invention can be increased.

Finally, a significant advantage of the method according to the invention is that empirical equations using a gold standard such as the Fick'schen principle for stroke volume, or eg echocardiography or isotope methods for other parameters, such as ejection fraction, pulmonary wedge pressure, diastolic function or the like. can be used for the measurement of haemodynamic parameters or underwater weighing or DXA methods or dilution methods for body water. These empirical equations can be obtained, for example, by means of partial correlations and multiple regression equations or else by means of neural networks or other "machine-learning" methods.

When two spaced voltage electrodes are used, the measuring voltage is determined at a first voltage electrode measuring length and at a second voltage electrode measuring length different from the first, and the measured values are used to determine the length of operation relative to a reference electrode for the impedance determination.

In order to be able to determine the distance between the voltage electrodes by measuring electrical variables, according to a further embodiment of the invention, the measuring voltage can be further determined at one of the first and the second different, third voltage electrode measuring length.

In addition, by attaching electrodes on the periphery or on the extremities or on the upper and lower end of the body, the total body impedance at different frequencies, and thus the body water can be determined with its sub-fractions such as extracellular space and intracellular space and it can from the relation of body water to the electrically participating chest volume further conclusions on the actual stroke volume and other hemodynamic parameters are obtained. If, in addition, limbs with different frequencies are also measured, there is also the opportunity to determine the intracellular space and extracellular space and also to introduce these values and their relation to one another into an equation for the calculation of CO. After intracellular space and extracellular space have been characteristically altered in heart disease, further important conclusions about the function of the heart can be gained. Heart failure leads to a decrease in the intracellular space and an increase in extracellular space.

A further embodiment of the invention can therefore consist in that the measuring current is impressed via two current electrodes at the upper and lower ends of at least one body extremity, eg on one leg, eg on the ankle, and / or on one arm, eg on the wrist becomes.

All substances involved in the impedance measurement in the body are subject to a frequency dependence, which can provide valuable information on the constitution of the organism to be measured.

Therefore, the measurement current should be impressed at different measurement frequencies and the associated measurement voltage values and their changes should be determined over time, especially over the time of the cardiac cycle. The frequencies used should give a measurable change in the blood impedance values.

An advantageous signal-to-noise ratio of the measured value determinations can be achieved if, in a further embodiment of the invention, the measuring current is impressed at a plurality of different voltage electrode measuring lengths and at a plurality of different measuring frequencies and the measuring voltage caused by the measuring current is measured.

Furthermore, determining the character of the impedance (inductive or capacitive) may prove to be beneficial in determining the phase angle between the measurement current and the measurement voltage.

Furthermore, it is advantageous if amplitudes, areas and rise or fall tangents of the impedance waves B, C, X and O are used individually or jointly for the calculation of haemodynamic parameters.

A further variant of the method according to the invention can be that the serum sodium is determined and used to calculate the parameters of interest.

The concentration of serum sodium can also be mathematically estimated by the method according to the invention and output as a result.

Furthermore, the hormones, e.g. ADH and Natriuretic Peptide, especially the Atrial Natriuretic Hormone, the "brain Natriuretic Peptide" and their precursors, which regulate the body water, its fractions and its composition, are estimated by the method according to the invention with the aid of empirical equations and output as a result.

Utilizing modern communication means, the processing of the data obtained from the method according to the invention can be done in such a way that the results of the method are sent digitally to a central location, preferably by telephone or email, where they are further billed and assessed, and that the Patients are informed of the necessary measures and therapy changes from a remote location.

Furthermore, the invention relates to a device for measuring the electrical impedance or its temporal change in a human body, in particular for a Elektromechanocardiographie- or impedance cardiography (IKG) measurement for the determination of hemodynamic parameters.

According to the invention, the object of the invention already defined is achieved in that two voltage electrodes are provided, of which at least one of the two is designed as a double-voltage electrode element, wherein the impedance and its change after the time between the two voltage electrodes can be tapped.

With the aid of a voltage electrode in the form of a double-voltage electrode, which has two electrodes arranged at a known distance from each other, the difference between two electrode measuring lengths with respect to the other voltage electrode is determined, so that from two measured at the double voltage electrode measuring voltages an operative electrodes Measuring length can be determined.

An adaptable to the body shape of the embodiment of the double-voltage electrode element can be achieved if the at least one double-voltage electrode element is applied to a common, insulating support film.

In a further embodiment of the invention, at least one of the voltage electrodes can be formed from a triple-electrode element consisting of a current electrode and two voltage electrodes. In this way, the introduction of the alternating measuring current and the tapping of measuring voltages in carrying out the method according to the invention can take place on a single electrode element. In particular, the current electrode and the double voltage electrode element can be applied as a triple electrode element on a common carrier foil.

In order to be able to carry out the impedance measurement according to the method according to the invention without manual switching or switching, it can further be provided that all terminals of the electrode elements are brought together via connecting lines in a distributor piece, and that the distributor piece is connected to measuring lines and control lines of a measuring device.

Another possibility of automating the method according to the invention may be that the distributor piece is controllable, so that the electrode elements can be connected to different measuring lines and control lines of the measuring device.

Since the various impedance values measurable by the measuring system according to the invention depend on the position of the human body in space, it is advantageous to record the angle between the body longitudinal axis and the horizontal or vertical. A further embodiment of the measuring system according to the invention can therefore consist in that a protractor is provided for measuring the body inclination. This may preferably on the manifold be arranged.

The invention further relates to a medical electrode element for measuring the electrical impedance or its temporal change in a human body, in particular for an electromechanocardiography or impedance cardiography (IKG) measurement for the determination of haemodynamic parameters, with a first current electrode, the a current terminal for impressing an alternating electrical measuring current, and a spaced therefrom, the first voltage electrode having a voltage terminal for tapping an electrical measuring voltage, wherein at least one further voltage electrode is provided with a voltage terminal , and wherein the at least one further voltage electrode is arranged at a distance from the first voltage electrode or for carrying out the method according to the invention, wherein the first voltage electrode and the at least one further voltage electrode are in the form of mutually parallel, electrically conduct the strip is formed, and the strip width is equal to or preferably smaller than the distance between the strips.

The strip-shaped design of the electrodes results in a relatively high measurement volume, e.g. Within the thorax, meaningful measurements can be made to determine body impedance.

Thus, in contrast to the conventional four-point method (two current electrodes and two voltage electrodes), there is at least one additional voltage electrode or possibly also additional current electrode which is or are attached to the body in such a way that the attachment of this additional voltage Electrode and / or current electrode results in a change in the measuring length L between the voltage electrodes or the place of introduction of the current at least two attached to the body of the patient electrode elements, preferably in the longitudinal direction of the body and thus in the main flow direction of the blood and that at the same time or alternately measuring the impedance and their change over time over the examined body segment - can be done in each case with the shorter and longer gauge length between the respective electrodes.

By introducing additional degrees of freedom, namely different measurement lengths between the voltage electrodes and also current-carrying electrode pairs, the actually electrically participating "operative thorax length" or the actually participating "thorax" or actually measured "operative specific resistance" of the blood can be solved of equations with several unknowns electrically determine or even bring with empirically obtained equations this additional knowledge in a so-called "black box" model. So only more electrically measured quantities enter into this formula. The problem of body size, namely that the stroke volume and other haemodynamic parameters are only correctly determined in the healthy person on the basis of the anthropometric preliminary information, is thus eliminated.

A possible further embodiment may now be that the at least one further voltage electrode is formed by a second voltage electrode, which is arranged in a known, constant or calculable distance (d) to the first voltage electrode.

Thus, the measured voltage with respect to a reference voltage electrode, which is mounted in another region of the body, on the one hand on the first voltage electrode and on the other hand tapped on the second voltage electrode and from the measurements thus obtained at a known distance d between the first and the second voltage electrode, an operative measurement length to the reference voltage electrode for the impedance value determination are determined.

The distance d between the first and second voltage electrodes is known by the shape of the electrode element according to the invention, but it has become known as possibly additionally highlighted, as well as in the operative measurement length to determine an operative distance between the first and the second voltage electrode.

This can be achieved according to a further embodiment of the invention in that the at least one further voltage electrode is formed by the second voltage electrode and a third voltage electrode, wherein the third voltage electrode arranged at a distance from the first voltage electrode is.

When using band electrodes, it has been found that a very high degree of reproducibility of the values measured with the electrode element according to the invention is given if the ratio of the strip length to the electrode spacing in the range between about 2, preferably 4 and about 15, is preferred 10 lies.

In this case, the distance between the individual electrodes according to a further embodiment of the invention can be kept constant by the first voltage electrode and the first current electrode and the at least one further voltage electrode and / or the at least one further current electrode a common electrically insulating substrate are arranged.

The carrier material may be formed by a carrier foil, wherein the first voltage electrode and the first current electrode and the at least one further voltage electrode and / or the at least one further current electrode are applied to one side of the carrier foil and preferably with an electrically conductive adhesive layer are provided. In this way, a constant spacing of the individual electrodes on the body surface is ensured during the implementation of the method according to the invention.

Another variant of the invention may consist in that the carrier material comprises a plurality of film strips with an adhesive surface, on which the first voltage electrode and the first current electrode and the at least one further voltage electrode and / or the at least one further current electrode are applied, and in that the film strips with the thereon Adhere electrodes in a substantially parallel arrangement on a common base support film, which base support film after application of the film strip on the body surface of these is removable. After removing the base carrier film, only the foil strips with one electrode each remain on the patient's body, which are in electrical contact with the body surface. While this leaves a constant spacing between the individual electrodes, the result is a significant reduction of skin irritations due to the small total contact area, which is why the electrodes can be left in contact with the patient for a longer time.

In order to achieve the most reliable and easy-to-use connection with the connecting cables required for operating the electrode element according to the invention, the carrier foil at one longitudinal end can taper on one side to a plug connection surface on which the first voltage Electrode and the first current electrode and the at least one further voltage electrode and / or the at least one further current electrode are guided closely spaced.

Another variant of the invention may consist in that the first voltage electrode and the first current electrode and the at least one further voltage electrode and / or the at least one further current electrode are designed in the form of spot electrodes which Spacers, eg also a carrier film or by a strained band or cable or rigid spacers are arranged spaced from each other. In this way, the measurement of the impedance can be made even over very small contact surfaces on the body surface.

Furthermore, the invention relates to a measuring system for measuring the electrical impedance or their temporal change in a human body, in particular for an impedance cardiography (IKG) measurement for the determination of hemodynamic parameters, with a measuring alternating current source and a first voltage measuring device and a medical electrode element according to the invention, wherein the measurement Power source with the current electrode and the voltage measuring device with the first voltage electrode of the electrode element are connectable.

In previously used measuring systems for measuring the electrical impedance in the body, the measuring length had to be between two electrode elements intended for the impedance measurement or at least the body size of the patient, e.g. with the help of a tape measure, to be measured. Due to measurement inaccuracies and due to the fact that the actual electrically acting measuring length deviates very much and in an unpredictable manner from the spacing to be measured on the body surface between the respective electrodes, distortions or inaccuracies in the determination of the measurement result occur.

The object of the invention is therefore to provide a measuring system of the aforementioned type, with which the aforementioned problems can be avoided.

According to the invention this is achieved in that a switch is provided, via which the voltage measuring device can be connected either to the first voltage electrode or to the at least one further voltage electrode. Alternatively, the measuring system can also be constructed in such a way that the measurement can take place simultaneously over different measuring lengths.

From the known distance between the first and the further voltage electrode, the effective effective against a reference electrode measuring length for determining the impedance of the impressed current and the tapped voltage values can be determined.

Since the result of the impedance measurement on the body of the patient is frequency-dependent, a further development of the invention consists in that the measuring alternating current source has a, possibly also continuously, variable measuring frequency. In this way, the influence of body components, such as blood, tissue and bone, on the measurement result at different measurement frequencies can be determined.

In this context, a phase detector for determining the phase angle between the measuring current of the measuring current source and the measuring voltage measured by the voltage measuring device can be provided, so that a further measured variable can be obtained with the phase angle.

Since the various impedance values measurable by the measuring system according to the invention depend on the position of the human body in space, it is advantageous to record the angle between the body longitudinal axis and the horizontal or vertical. A further embodiment of the measuring system according to the invention can therefore consist in that a protractor is provided for measuring the body inclination. This can preferably be arranged in a manifold.

The measuring electrodes of the measuring system according to the invention can also be used for other purposes, wherein it appears to be particularly advantageous if the electrode elements are connected according to a further embodiment of the invention with an ECG measuring device.

Since the electrode element according to the invention described here and the method according to the invention that can be carried out here have little similarity to the previous impedance cardiography, the new method "multi-site frequency electromechanocardiography (msf-ELMEC)" is proposed for the method and measuring system described here according to the invention. all of them electrically determinable parameters of cardiac output, such as stroke volume, inotropy, ejection fraction, diastolic cardiac function, valvular abnormalities and potentially other hemodynamic parameters such as pulmonary pressure and other important parameters such as volume that determine distribution, composition of different body compartments.

• Fig.3 ein Diagramm, das den Zusammenhang zwischen der am Körper gemessenen Messlänge und der ermittelten operativen Messlänge zwischen zwei Spannungs- oder Strom-Elektroden wiedergibt;
• Fig.4A ein Diagramm, aus dem ein Vergleich der Herzschlagvolumensbestimmungen nach der herkömmlichen Impedanzkardiographie- und der Rebreathing-Methode hervorgeht;
• Fig.4B ein Diagramm, aus dem ein Vergleich der Herzschlagvolumensbestimmungen nach der erfindungsgemäßen Impedanzkardiographie (msf-ELMEC)- und der Rebreathing-Methode hervorgeht;
• Fig.5 zeigt ein nach der Zeit abgeleitetes Impedanzsignal, ein Elektrokardiogramm und und ein Phonokardiogramm eines Patienten;
• Fig.6 ein nach der Zeit abgeleitetes Impedanzsignal für einen gesunden und einen erkrankten Patienten im Vergleich;
• Fig.7 eine Ausführungsform des erfindungsgemäßen Elektroden-Elements;
• Fig.8 eine weitere Ausführungsform des erfindungsgemäßen Elektroden-Elements;
• Fig.9 eine schematische Darstellung einer Ausführungsform des erfindungsgemäßen Messsystems;
• Fig.10 eine weitere schematische Darstellung einer Ausführungsform des erfindungsgemäßen Messsystems;
• Fig.10a ein Detail einer Weiterbildung des erfindungsgemäßen Messsystems nach Fig.10;
• Fig.10b ein Detail einer Weiterbildung des erfindungsgemäßen Messsystems nachFig.10;
• Fig.11 eine schematische Darstellung einer weiteren Ausführungsform des erfindungsgemäßen Messsystems;
• Fig.12 eine schematische Darstelllung einer weiteren Ausführungsform des erfindungsgemäßen Messsystems und
• Fig.13 eine schematische Darstellung einer weiteren Ausführungsform des erfindungsgemäßen Messsystems.

The invention will be explained in detail with reference to the embodiments shown in the accompanying drawings. It shows

• Figure 3 a diagram showing the relationship between the measurement length measured on the body and the determined operative measurement length between two voltage or current electrodes;
• 4A a diagram showing a comparison of the heartbeat volume determinations according to the conventional impedance cardiography and rebreathing method;
• 4B a diagram showing a comparison of the heartbeat volume determinations according to the impedance cardiography (msf-ELMEC) - and the rebreathing method according to the invention;
• Figure 5 shows a time-derived impedance signal, an electrocardiogram and and a phonocardiogram of a patient;
• Figure 6 a time-derived impedance signal for a healthy and diseased patient in comparison;
• Figure 7 an embodiment of the electrode element according to the invention;
• Figure 8 a further embodiment of the electrode element according to the invention;
• Figure 9 a schematic representation of an embodiment of the measuring system according to the invention;
• Figure 10 a further schematic representation of an embodiment of the measuring system according to the invention;
• Figure 10a a detail of a development of the measuring system according to the invention Figure 10 ;
• 10B a detail of a development of the measuring system according to the invention Figure 10 ;
• Figure 11 a schematic representation of another embodiment of the measuring system according to the invention;
• Figure 12 a schematic representation of another embodiment of the measuring system according to the invention and
• Figure 13 a schematic representation of another embodiment of the measuring system according to the invention.

In the method according to the invention for measuring the volume, the composition and movement of electrically conductive body fluids, based on the electrical impedance of the body or a body segment, in particular for the electromechanocardiography (ELMEC) or impedance cardiography (IKG) measurement for the determination of haemodynamic parameters , an alternating measuring current of at least one frequency is introduced into the body, and the impedance and its change over the time of substantially the same body segment through which the alternating measuring current flows are measured at at least two different measuring lengths essentially in the longitudinal direction of the body.

In particular, for an impedance cardiography (IKG) measurement to determine haemodynamic parameters, e.g. of the heartbeat volume, an alternating measuring current is impressed via current electrodes, which are spaced apart from one another on the body surface by a current electrode measuring length, and by means of voltage electrodes which are spaced apart on the body surface, in particular on the thorax surface, by a voltage electrode measuring length are tapped, caused by the measuring current measurement voltage.

From the measuring current and the measuring voltage, the electrical impedance or its temporal change is calculated.

In the method according to the invention, for example, the measuring voltage becomes different Voltage electrode measuring lengths between the voltage electrodes on essentially identical body segment or segments determined. From the resulting measured voltage values, the associated impedance values are calculated. The change in the measuring length takes place mainly in the longitudinal direction of the body and thus in the main direction of the transported blood in this.

Furthermore, it is advantageous to determine the impedance or its change at at least two different measuring frequencies, better at least three to four frequencies. This presupposes that the measuring alternating current source used for the measurement has a variable, possibly also continuous, variable measuring frequency.

The measurement frequencies should be so far apart that a measurable change in the impedance of blood can be observed, or that at the higher frequency, a penetration of the body membranes by the electric current takes place. As relevant frequencies, for example, between 1 and 10 kHz, between 30 and 100 kHz, in particular about 40 kHz, and greater than 200 kHz, for example, about 300 kHz to 1 MHz called, this being only rough guidelines for the desired frequency range. Furthermore, instead of the measurement of individual frequencies, a "frequency sweep" may be proposed across the entire spectrum of interest, from a lower measurement frequency up to an upper measurement frequency, eg between approx. 1 kHz and approx. 1000 kHz or over an in to perform this section of interest. In order to keep the signal-to-noise ratio of the measurements low, it may prove advantageous to measure alternately or simultaneously at several lengths and several frequencies. Furthermore, it may prove convenient to co-determine the phase angle of the impedance signal with a special structure of the electronics. For this purpose, a phase detector is provided for determining the phase angle between the measuring current of the measuring current source and the measuring voltage measured by the voltage measuring device.

wenn p der spezifische Widerstand der Messstrecke, L die Messlänge und A der Querschnitt der Messstrecke ist.As is known, according to the definition of resistivity, the impedance is: $${\mathit{<figure-callout\; id="0"\; label="Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Z</figure-callout>}}_{\mathit{0}}=\rho *\left(L/A\right)$$

if p is the resistivity of the measuring section, L is the measuring length and A is the cross section of the measuring section.

vorhanden, wobei d ein konstanter oder berechenbarer Abstand zwischen beiden Messlängen L und L₂ ist, dann lässt sich sehr leicht ableiten, dass die operative elektrische Messlänge L_o nach folgender Formel errechnet werden kann: $$L_o=\frac{d}{\frac{Z_{02}}{Z_{01}}-1}$$

Is now a second measuring section with the measuring length $$L_{}$$$${}_{\mathit{2}}=L+d$$

If d is a constant or calculable distance between the two measuring lengths L and L ₂ , then it can be easily deduced that the operative electrical measuring length L _o can be calculated according to the following formula: $$L_O=\frac{d}{\frac{Z_{02}}{Z_{01}}-1}$$

If, for example, this electrically measured measuring length L _{o is included} in the KuBICEK equation, then all unknown length measures have disappeared from the formula except for the difference d (electrode spacing) defined exactly by the shaping of the electrodes.

In a device for measuring the electrical impedance or its temporal change in a human body for the determination of body fluids, their composition and their displacement in the body, eg haemodynamic parameters according to the invention two voltage electrodes 8a, 80 and 81, 82, 80 ', 81' , 82 ', 85, 85', 85 ", 7, at least one of which is designed as a double-voltage electrode element 80, 81, 82, 81 ', 82', 85, 85 ', 85", wherein the impedance and its change after the time between the two voltage electrodes can be tapped. In Fig. 9 For example, the one voltage electrode is formed by a triple electrode element 80 and the second voltage electrode is formed by two triple-electrode elements 81, 82 mounted at the same height.

The construction of the triple-electrode elements 80, 81, 82, namely a current electrode 70 and two voltage electrodes 72, 73, which form a double-voltage electrode element, is shown in FIG Figure 7 in which the current electrode 70 and the two voltage electrodes 72, 73 are mounted at a constant and known distance from one another, preferably to maintain the constant distance on a common carrier foil 2.

Although the difference d is known from the shape of the electrodes 72, 73, it may as well be electrically invalid as the length L measured at the thorax surface. Therefore, it can prove to be additionally favorable, by appropriate wiring of the existing measuring electrodes in analogy to the calculation of L _o according to formula (9) to calculate an operative d _o . Since it is favorable to perform no interventions on the inhomogeneous current field within the thorax in these calculations of operative lengths, it is favorable to leave the current-carrying electrodes unchanged and to use only additional measuring electrodes.

For example, the calculation of a d _o makes it necessary to attach an additional measuring electrode 71 to an electrode element 80 according to the invention, as shown in FIG Figure 12 is shown, so that at the upper thorax aperture then a quadruple electrode element, namely a current electrode 70 and three voltage electrodes 71, 72, 73 are arranged. The measuring current is impressed via a measuring alternating current source 52, which is connected between the current electrode 70 and a current electrode 60 of an electrode element 20, which is applied, for example, to the lower thorax aperture. If the current is impressed, for example, at the lower end of the patient's body 7 or at the lower end of the trunk 85, 85 ', a three-electrode element with three is also sufficient Voltage electrodes, which may optionally be attached to either the lower or upper thoracic aperture.

A voltage measuring device 51 is connected on the one hand to a voltage electrode 61 of the electrode element 20 and connected via a changeover switch 50 either to the first voltage electrode 73 or to another, namely the second and the third voltage electrode 72, 71 , The measuring length between the voltage electrode 61 and the first voltage electrode 73 is L, the measuring length between the voltage electrode 61 and the second voltage electrode 72 is L2, and the measuring length between the voltage electrode 61 and the third voltage electrode 71 is finally equal to L3. Furthermore, L2 = L + d and L3 = L + d1.

By controlling the switch 50, a total of three measuring voltages can be tapped, which correspond to the measuring lengths L, L2 and L3.

After calculating d _o , this value can then be substituted into equation (9) instead of d.

A variant of the measuring system according to the invention, in which a plurality of current electrodes are provided instead of a plurality of voltage electrodes, is disclosed in US Pat Figure 13 shown.

The starting point in turn is a quadruple electrode element 80, on which a voltage electrode 33 and three current electrodes 30, 31, 32 arranged at a defined distance from one another are provided. The measuring length between the current electrode 60 of the electrode element 20 and the current electrode 32 is L, it increases to L4 for the current electrode 31 and to L5 for the current electrode 30, where L4 = L + a and L5 = L + a1.

The measuring current is via the measuring alternating current source 52, on the one hand to the Current electrode 60 of the electrode element 20 connected and on the other hand via the switch 50 to the current electrodes 30, 31, 32 is switchable, impressed.

The voltage measuring device 51 is connected to the voltage electrode 61 of the electrode element 20 and connected to the voltage electrode 33, so that the impedance and an operative measurement length can be determined by voltage measurement at three different measurement lengths L, L4 and L5 of the current injection arising from analogous considerations to the embodiment according to Figure 11 results.

Fig. 3 shows the differences between the actual measured length in cm measured on the body surface in practical experiments and the "operative length" L _o calculated from Ohm's law for a prior art electrode element. As can be seen, the relationship between the two lengths is extremely unsatisfactory, indicating that there is no clinically relevant relationship between the length measured on the body surface and the operative length, as shown by the formula given above. Above all, you can in the Fig. 3 observe that the measured length is significantly longer than the virtual length, indicating that there must be substantial changes in the diameter of the electrically participating thoracic tissue between the electrodes, apparently shortening the virtual electrode gap as "electric bellies", and not to be expected Wise.

It can thus be seen that so far impedance impedance cardiography was based on completely wrong theoretical considerations. This is very easy to explain because the distribution of electricity in the thorax is extremely inhomogeneous, and the conduction through the different media such as skin, bone, fat, lung, heart and vessels are distributed differently. So far, the reproducibility of the impedance cardiography was also very limited by these inhomogeneities. In order to be reasonably reproducible, the electrodes had to be placed as exactly as possible at the same place on the thorax. This is possible in the short-term test, but not at Long-term observations over days or longer. With the method according to the invention this has become independent of the place of application of the electrodes, because the method automatically corrects automatically by measuring the operative measuring length, even if the conditions within the thorax should have changed, eg by a different liquid distribution.

A very advantageous method is also the attachment of the current-carrying electrode to the extremities 7, 8a, because of them, the current takes place mainly along the large vessels and along the aorta. The measuring current is thereby applied via two current electrodes to at least one body extremity, e.g. embossed on one leg and / or on one arm.

This results in a much more homogenous current field in the thorax than when the current-carrying electrode is attached directly to the thorax. Thus, at the lower thorax aperture, attachment of a double electrode would be sufficient, e.g. in the A392 / 2001 patent. When attaching two double electrodes, e.g. the electrode described in A392 / 2001 or two adjacent individual electrodes at the upper end of the body (for example neck, head or arms) or at the lower end of the body, the body fluid can then also be measured at the same time, ie the total body impedance is also measured. This is important because the fluid content of the thorax must be considered in relation to the fluid balance of the organism. Especially in heart failure, the distribution of fluid in the thorax is very disturbed in relation to the total body fluid, which has hitherto made the application of impedance cardiography in heart failure impossible.

Another major problem of impedance cardiography is the involvement of specific blood resistance, which should be quantitatively incorporated into the formula. Therefore, at least in the KUBICEK equation, the specific blood resistance calculated from the hematocrit is included in the formula. QUAIL ET AL. [ ^xi ] wrote the KUBICEK equation and calculated the resistivity from the stroke volume and other haemodynamic parameters that they determined using an electromagnetic flowmeter (EMF) in dogs: $${\mathrm{\rho }}_{\mathrm{blood}}\mathrm{=}\frac{{\mathrm{SV}}_{\mathrm{ELEVEN}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Z</figure-callout>}}_{\mathrm{0}}^{\mathrm{2}}}{{\mathrm{1}}^{\mathrm{2}}\mathrm{\cdot }\mathrm{LVET}\mathrm{\cdot }\mathrm{(}\mathrm{dZ}\mathrm{/}\mathrm{dt}{\mathrm{)}}_{\mathrm{Max}}}$$

QUAIL ET AL. found that although ρ _blood is dependent on hematocrit, it otherwise remains approximately constant. They replaced ρ _blood with a mean thoracic resistance ρ ₀ . If ρ _{0 is} approximately a constant in KUBICEK's equation, it can be replaced as follows: $$\mathrm{Z}\mathrm{=}\mathrm{\rho }\mathrm{\cdot }\frac{\mathrm{1}}{\mathrm{A}}\mathrm{<figure-callout\; id="0"\; label="\Rightarrow \; \rho "\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\Rightarrow \; </figure-callout>}{\mathrm{\rho }}_{}{\mathrm{}}_{\mathrm{0}}\mathrm{=}\frac{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Z</figure-callout>}}_{\mathrm{0}}\mathrm{\cdot }\mathrm{A}}{\mathrm{1}}$$

Now put in KUBICEK's equation: $$\begin{array}{l}\mathit{SV}=\frac{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0\cdot A}{l}\cdot \frac{l^2}{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0^2}\cdot \mathit{LVET}\cdot (\mathit{dZ}\mathit{/}\mathit{dt}{)}_{\mathrm{Max}}\\ \mathit{SV}=\frac{A\cdot \mathrm{<figure-callout\; id="0"\; label="l\; Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">l\; </figure-callout>}}{Z_{}}\cdot \mathit{LVET}\cdot (\mathit{dZ}\mathit{/}\mathit{dt}{)}_{\mathrm{Max}}\\ \mathit{SV}=V_{\mathit{thorax}}\cdot \mathit{LVET}\cdot \frac{(\mathit{dZ}\mathit{/}\mathit{dt}{)}_{\mathrm{<figure-callout\; id="0"\; label="Max\; Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Max\; </figure-callout>}}}{Z_{}}\end{array}$$

We have now mathematically eliminated the very elusive resistivity (resistivity p) from the stroke volume and other hemodynamic parameters. The prerequisite for this is that this specific blood resistance remains constant during cardiac activity. After SHANKAR ET AL. [ ^xii ] the change in resistivity depending on the activity of the heart is less than 5.5% and thus the equation is sufficiently accurate.

An alternative would be to use p at different times Heart activity measures, for example, at the time of maximum blood flow, during systole, as well as at the time of minimal blood flow, at the end of diastole. It is better to observe the impedance change after the time (dZ / dt) _max , as is usual with impedance cardiography, since this value is determined by the action of the heart and thus by the amount of blood from the heart (SV). For the new method, only the property has to be used that the specific resistance of the blood p, especially of the red blood cells (erythrocytes), is different at different frequencies of the alternating current. Thus, for example, the electrical resistance of the blood at 20 kHz is significantly higher than for example at 100 kHz, at even higher frequencies, the conductivity of the erythrocytes still further increases, because at higher frequencies, the erythrocyte membrane behaves like an electrical capacitor. This property can then be exploited to determine p; more precisely, the decrease in (dZ / dt) _max at higher frequencies is a measure of the number of red blood cells, that is, the specific resistance of the blood associated with the hematocrit. The greater the decrease of (dZ / dt) _max in the transition from a low to a high frequency, the greater the number of red blood cells, since the stroke volume remains the same for the specific heartbeat. $$\rho =f\left(\mathit{Hkt}\right)=F\left(\frac{({}^{\mathit{dZ}}{\mathit{/}}_{\mathit{dt}}{)}_{\mathrm{Max\_}\mathit{freq}1}}{({}^{\mathit{dZ}}{\mathit{/}}_{\mathit{dt}}{)}_{\mathrm{Max\_}\mathit{freq}2}}\right)$$

Similarly, in nonlinear relationships, more than 2 frequencies may be measured, and any functions that may result from this may also be expressed as a non-linear regression equation. The function F can be determined empirically in both cases (2 frequencies, several frequencies) by comparison measurements with the conventional determination of the hematocrit Hkt.

Another method to come from electrically measured signals on the change in blood resistance during the cardiac cycle is also apparent from the above method: WANG ET. AL. [ ^Xiii ] have shown that the change in blood resistivity ^- 25% of the impedance change, is therefore a significant measure of the calculation of the right SV. This blood resistivity change is now a direct measure of the ratio between the two differentiated impedance signals measured at different frequencies (dZ / dt) _freq1 / (dZ / dt) _freq2 . Thus, an additional signal Δρ (t) = (dZ / dt) _freq1 / (dZ / dt) _freq2 can now be obtained continuously, which represents a measure of the blood _resistance change during the cardiac cycle. For this, for example, only a sliding narrow window would have to be placed over the cardiac cycle in order to determine the Δρ (t) for each of these narrow windows. The maximum deflection of this signal Δρ _max can now also be used for the determination of the CO. So it is not absolutely necessary to empirically determine the function F beforehand. $$\mathrm{\Delta }\rho \left(t\right)=\frac{(\mathit{dZ}/\mathit{dt}{)}_{\mathit{freq}1}}{(\mathit{dZ}/\mathit{dt}{)}_{\mathit{freq}2}}$$

An additional advantage of the method is that with sufficiently precise determination of the Δρ (t) signal according to the above method, it is now also possible to determine whether the blood is flowing or not and what type of flow it is. Namely, in the case of laminar flow, the resistance decreases as a result of alignment of the erythrocytes in the direction of flow, in order to increase again at higher speed as a result of the turbulence. It can then be determined from the shape curve of the continuously measured Δρ (t) values how long the blood is flowing and whether the flow of the blood is laminar or turbulent. Thus, the LVET (left ventricular ejection time), which is conventionally determined from the IKG signal directly or from the phonocardiogram, could also be determined by a measurement from the changing p.

The exact determination of the blood resistivity p, the correct operative length L ₀ , or the basic impedance Z _o , which is a measure of the thorax geometry, is necessary for the determination of the correct SV, because from these quantities, the correct determination of the derive electrically participating thoracic volume V _thorax . This electrically participating chest volume V _thorax is the important measure for the determination of SV with the help of impedance cardiography, as can be seen from the general equation of the IKG (12c): $$\begin{array}{c}\mathit{SV}=V_{\mathit{thorax}}\cdot \mathit{LVET}\cdot \frac{(\mathit{dZ}\mathit{/}\mathit{dt}{)}_{\mathrm{<figure-callout\; id="0"\; label="Max\; Z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Max\; </figure-callout>}}}{Z_{}}\end{array}$$

As described earlier, KUBICEK calculates this V _thorax from the electrode distance L, the resistivity of the blood p and the basic impedance Z ₀ , SRAMEK or AMBER further estimate V _thorax from the height H and / or the weight of the patient W. Further "improved" Formulas used on a variety of ICG devices even process the patient's age to determine the V _thorax .

However, these values, or linear dependencies of these values, can now be determined from electrically measurable variables as described above. Thus, the V _{thorax can} only be determined from different electrical quantities. $$\begin{array}{l}{V}_{\mathit{thorax}}=f\left(L,,\rho ,,Z_O,,H,,W\right)\\ V_{\mathit{thorax}}=f(\frac{d}{\frac{Z_{02}}{Z_{01}}-1}.\frac{({}^{\mathit{dZ}}{\mathit{/}}_{\mathit{dt}}{)}_{\mathrm{Max\_}\mathit{freq}1}}{({}^{\mathit{dZ}}{\mathit{/}}_{\mathit{dt}}{)}_{\mathrm{Max\_}\mathit{freq}2}}.\frac{Z_{\mathit{freq}1}}{Z_{\mathit{freq}2}}.\frac{Z_{\mathit{freq}1}}{Z_{\mathit{freq}3}}....)\end{array}$$

These quantities, which are now only electrically measured, can be incorporated not only into any known formula for determining the stroke volume and other hemodynamic parameters, such as the formulas of KUBICEK, SRAMEK or BERNSTEIN, but also into any equation for determining the stroke volume and other hemodynamic parameters ; These could be not derived but empirically derived equations, which can be compared with a gold standard such as the invasive Fick 'principle, the thermodilution or the breathing gas method are obtained. Thus, only more electrically measured quantities remain in the equation, resulting in a much greater precision. The quality of the individual signal is of subordinate importance, since it can be measured at each heartbeat, ie approximately 70 times a minute, and the values calculated from each individual heartbeat are either averaged or an exact template determined from the impedance signal.

Similarly, the electrically determined parameters L and p may be introduced into any known or newly developed equation for calculating the stroke volume and other hemodynamic parameters. Also, the numerous parameters thus electrically determined may also be used to calculate other important parameters of the mechanical cardiac function, e.g. the ejection fraction, contractility, inotropy, pulmonary pressure, etc. may be used.

In our experience, it has at least been proven to use empirical formulas for stroke volume and other hemodynamic parameters, such as ejection fraction, inotropy, etc., that are constructed using the gold standard for the sizes listed above. The variables Z ₀₁ , Z ₀₂ , (dZ / dt) _{max_freq1} , (dZ / dt) _max _ _freq2 , Z _freq1, Z _freq2 , Z _freq3 ,..., _{Could be determined} , preferably in a multiple regression analysis and / or with neural Meshes and / or other machine learning algorithms with the actual stroke volume and other haemodynamic parameters obtained by a gold standard method. Of course, the gold standard for the actual stroke volume and other hemodynamic parameters would be the fuck From this, a multiple regression equation could be constructed, which purely empirically describes the best relationship between the above parameters and the actual beat volumes, so that all inhomogeneities would be biological Measurement, such as the fact that the thorax is not a geometrically defined body and that the homogeneity of electricity propagation in the thorax in the different tissues, such as fat, muscle, ribs, skin, lungs, vascular tapes and heart, never can be described mathematically sufficiently accurately. Because of the nonlinearities, a multiple polynomial equation can also result. Particularly important in these formulas is the use of whole-body impedance, and this at several frequencies, for example at about 1-10 kHz, 40 kHz and 200 kHz and possibly even at much higher frequencies, because thus the body water, the extracellular space and the Intracellular water and its relation to the fluid content of the thorax is taken into account. These formulas would include all the electrically measured quantities which, in a partial correlation analysis, have shown to be significantly related to the mechanical performance of the heart.

Fig. 4 shows, for example, a calculated using a simple application of the method presented here calculation of CO in an unselected patient, including patients with heart failure, which had to be due to a variety of diseases surgery. During the operation, was determined by the NICO device that ₂ rebreathing cardiac output measures on CO, and which has excellent accordance with the thermodilution in ventilated patients, measured cardiac output as a "Gold Standard". In the upper part of the figure, the correlation of NICO-CO with conventional impedance cardiography is shown on the x-axis. As can be seen, r = 0.58, which corresponds to a clinically very poor and thus unusable correlation (although the body measurements were included and so a mathematical prediction of the CO has been included). In the lower part of the figure, on the other hand, the comparison of the NICO-CO with a very simple version of the msf-ELMEC is shown without any use of input body parameters such as weight and size, where the correlation coefficient r = 0.84, which is already a clinical one corresponds to very useful correlation. This correlation can be found in more complex technical Improve execution significantly.

Fig. 5 shows the usual differentiated impedance signal, with the usual nomenclature, namely the time points A, B, C, X, Y and O, and the simultaneously registered ECG and phonocardiogram. The times of maximum blood flow are between RZ and the minimum blood flow just before the A wave. It should be noted that the impedance curves (ΔZ and dZ / dt) are reversed conventionally in the sign.

Another way to improve the msf-ELMEC results from the following approach:

Usually only the level of the dz / dt is currently used for the evaluation of the impedance cardiography, although much more information is hidden in the form of the impedance signal. Thus, in heart failure, the shape of the impedance signal changes as in Fig. 6 will be shown. In the upper part of the Fig. 6 is a dZ / dt signal of a healthy person to see in the lower part of the dZ / dt signal of a patient with heart failure. As can be seen, although in heart failure the (dZ / dt) _max (C-point) becomes smaller, in addition there are additional changes, such as an increase in the amplitude of the X-wave and the O-wave.

As shown in this figure, the amplitudes of the negative wave B, the positive amplitude of the wave C (the actual (dZ / dt) _max ), the negative wave X and the positive wave should possibly additionally instead of the sole (dZ / dt) _max O, also the associated rise and fall slopes and surface integrals are introduced into the formula.

In addition, it may be necessary to know the position of the human body in space along the longitudinal axis, since the different Z ₀ can also enter the equation differently in different positions. This can be as prove beneficial to co-determine the position of the body, for this purpose may be attached to the body of a protractor, which could be accommodated advantageously in the manifold example, so that it is hidden and can be used again in every patient. In this case, the equations for determining stroke volume and other hemodynamic parameters for the different body position would be corrected.

With all these innovations, the method seems to be physically accurate enough, exclusively electrically defined, of high precision and reproducibility and thus for the first time suitable for the diagnosis of heart disease and for monitoring in the intensive care and anesthesia field. In contrast to all other methods, only a few, comfortable electrical electrodes have to be applied to the thorax and the extremities, which are also available for the derivation of the ECG at the same time; it is no longer necessary to carry out questionable length measurements on the thorax, which can never be precise due to the asymmetrical shape of the thorax and the existing multiple electrodes with necessary averaging; it is no longer necessary to enter the patient's body size, which, as already explained, introduces unwanted bias-biasing bias into the equation; the patient no longer has to be catheterized into the pulmonary artery or other artery and no longer needs to breathe through a mouthpiece in a closed system. The application of a dye, which is measured transcutaneously, is thus superfluous.

Fig. 7 shows an example of expression of the necessary for this purpose electrode elements according to the invention.

On this, a first current electrode 70 has a current terminal 90 for impressing an alternating electrical measurement current, while at a spaced therefrom, the first voltage electrode 73, a voltage terminal 93 is designed for tapping an electrical measurement voltage.

According to the invention, a further, here a second, voltage electrode 72 with a voltage connection 92 is provided, which is arranged at a distance d from the first voltage electrode 73. Within the scope of the invention, it is also possible to provide a plurality of further voltage electrodes or a plurality of current electrodes.

The first voltage electrode 73 and the first current electrode 70 and the at least one further voltage electrode 72 are in the form of mutually parallel, electrically conductive strips which are arranged on a common electrically insulating carrier material, in particular a carrier foil 2. In this case, the first voltage electrode 73 and the first current electrode 70 as well as the second voltage electrode 72 are applied to one side of the carrier foil 2 and preferably provided with an electrically conductive adhesive layer.

To simplify the production of an electrical contact with a measuring current source or with a measuring voltage device further tapers the carrier film 2 at one longitudinal end on one side to a plug-in pad 6, on which the first voltage electrode 73 and the first current -Electrode 70 and the second voltage electrode 72 are guided closely spaced. The carrier film 2 is preferably made of a skin-compatible, non-conductive, pliable material and can be made continuous between the electrodes 70, 72, 73, as in the embodiment according to Figure 7 is shown.

In the embodiment according to Figure 8 In contrast, the carrier material comprises a plurality of film strips 3 with an adhesive surface, to which the first voltage electrode 73 and the first current electrode 70 and the at least one further voltage electrode 72 are applied, the film strips 3 with the electrodes 70 thereon, 72, 73 in a substantially parallel arrangement on a common base support film 4 adhere, which base support film 4 after application of the film strip 3 on the body surface of these is removable.

The constant distance between the electrodes 70, 72, 73 is thereby ensured that the base carrier film 4 is removed again after its attachment to the thorax. This has the advantage that a skin irritation of the large area of a very wide carrier film 2 of the embodiment according to Figure 7 is reduced to a very small area.

This in Figure 8 The electrode element 80 according to the invention has, in a known manner, preferably on the side facing the body, initially a peel-off film which keeps the conductive coating of the electrodes 70, 72, 73 and the non-conductive adhesive of the base carrier film 4 moist and only immediately before use is withdrawn, as is well known from all medical electrodes.

Of course, additional voltage and current electrodes could additionally be applied to this carrier foil 4, eg also an additional current electrode or additional voltage electrodes in order to mathematically calculate the operative electrode measuring length L _o or the operative distance d _o . On the other hand, the use of a common current electrode 70 has the advantage that the electric field in the thorax, both when measuring Z ₀₁ and Z ₀₂ , can not change in its inhomogeneity.

A further embodiment of the electrode element according to the invention for ensuring the constant distance may be that an additional carrier film is attached to the side facing away from the body, which is removed only after attachment of the finger-shaped carrier film on the thorax. The carrier-carrier film should therefore also have no skin-irritating adhesive on the surface between the carrier films.

Like from the Fig. 8 Furthermore, the electrodes 70, 72, 73 in the region of a connector 7 for an impedance measuring device are preferably in one side tapered 6 of the film strips 3 merged so as to be able to use here a narrow, practical in clinical practice and cost-effective connector 7.

Fig. 9 shows a measurement setup on the body of a patient with the involvement of the measuring system according to the invention. At the distal ends of extremities, such as arms and legs, are mounted electrode elements 7 and 8a which best serve to measure whole body impedance at two, three or more frequencies and include both current and voltage electrodes. In order to avoid an asymmetrical current distribution within the body, in the illustrated embodiment, the attachment of the electrode elements 7 and 8a takes place on both legs and on both arms, wherein the impressed current is chosen to be the same size in each body half. Alternatively, a measuring current could be introduced via just one arm and only one leg.

At the lower thorax aperture, the two triple-electrode elements 81, 82 and in the neck region, the triple-electrode element 80, each with a voltage electrode and two current electrodes are further attached. A measuring current is impressed via the current electrode of the upper (neck region) triple-electrode element 80 and the current electrode of the lower electrode elements 81 at the lower thorax aperture, as well as between the current electrode of the upper triple electrode element 80 and the lower triple electrode element. Electrode element 82, wherein the measuring current flowing through the left half of the body and the measuring current flowing through the right half of the body are preferably selected to be equal. By attaching the left and right lower electrode members 81, 82, a relatively large body volume is detected by the measurement. Alternatively, only one electrode element extending over the entire body front side at the lower thorax aperture could be provided, but it has been shown that two electrode elements 81, 82 arranged next to one another, as shown in FIG Figure 9 shown to allow a better reproducibility of the measurement results. The measuring voltages are on the associated first and second voltage electrodes of the electrode elements 80, 81, 82 tapped and further processed to determine haemodynamic parameters in accordance with the invention.

All connections of the electrode elements 7, 8a, 80, 81, 82 (and also the in Figure 10 shown electrode elements 80 ', 81', 82 ', 85, 85', 85 ") are brought together via connecting lines 10 in a manifold 9, which is fixed on the body of the patient and includes a protractor 11, which is used to determine the position of the patient's body Of course, the protractor 11 could also be located elsewhere on the patient's body or on the couch on which the animal is located is via a connected to the manifold 9 measuring and control line 10a in a position all circuits of the voltage electrodes and also the current electrodes of the electrode elements 7, 8a, 80, 81, 82, 85 automatically by, for example, an analog Make switch 13.

The electrode elements 80, 81, 82, 81 ', 82', 85 ', 85 "may have, in addition to a first and a second voltage electrode, a third voltage electrode or further voltage electrodes.

It is equally conceivable, of course, to apply the known circular electrodes in a triple or multiple design to the body, or also to aim for a triple or multiple embodiment for sputter electrodes. Also, any other electrode shape would have to be designed so that there is a variable distance at least between the current or voltage electrodes.

Another, for example, electrode arrangement for feeding the current in the periphery is in Fig. 10 shown. As can be seen, the two triple electrode elements 81, 82 at the lower thorax aperture of the embodiment according to Figure 9 are replaced by corresponding Zweifachelektrodenelemente 81 ', 82', since the current is introduced via an electrode 7 further peripherally, these dual electrode elements 81 ', 82' must then be connected as a double voltage electrodes to the impedance of the substantially identical thorax segment at two different distances to eat.

Additionally shows Figure 10 a possibly also additionally to be attached Zweifachelektrodenelement 85 at the bottom of the fuselage approximately at the level of the step. Alternatively, in Figure 10a the placement of a triple electrode element 85 'at the lower end of the fuselage where, alternatively, the current can also be introduced and thus the impedance history of the fuselage can be measured at two different distances. This electrode element 85 or 85 'can be embodied either as a double or triple electrode element, possibly short-circuited, on the left or right of the fuselage, or only on one side of the fuselage. This electrode arrangement has the advantage that the impedance of the limb can also be measured at two different distances, so that here too an operative length or an electrically participating volume can be calculated. This could also be, for example. combine with an optional additional dust barrier 86 at the extremity, so as to additionally measure in a known manner plethysmographically the arterial and venous perfusion. For measuring the venous perfusion, only the dust level should be inflated to about 40 mm Hg, which is below the arterial pressure but higher than the venous pressure, in order to calculate the increase in volume of the leg from the impedance change. To measure the arterial blood flow, the dust container would be inflated to values higher than the arterial blood pressure and then analyze the change in impedance after opening the dust cover. This also brings a significant improvement of these methods, which could previously indicate the circulation change only as a change in impedance in percent. With the aid of the calculated electrically participating volume, volume change in absolute volume, eg in milliliters, can now also be indicated. Since essentially both legs have the same volume, could also Double-sided measurement on both legs omitted and the electrode element 7 only at the periphery of a limb as in Fig. 10 be shown attached. This single electrode element could then be connected to a single electrode element 85 or 85 ', or as in FIG 10B If the impedance of the legs is not of interest, an electrode element 7, which includes only a single current electrode but no voltage electrode, could also be mounted Fig. 10 shown omitted.

This is possible because the arms contain only a small, and very constant proportion of the electrically conductive Körperflüßigkeiten so that even without direct measurement of the arms, can be extrapolated from the measurement of the rest of the body on the total body impedance and thus on the total body fluids. This has the advantage that despite monitoring the patient with the method and apparatus of the application, the arms remain free for use by the patient and are also available for other medical needs, which is particularly appreciated in intensive care units. Therefore, in the present application, the neck, the upper thorax aperture, the arms, and also the head as the upper body end are optionally meant when writing from the upper end of the body.

Optionally, either the left and / or the right electrode elements 81, 82, 81 ', 82' could be switched off at the lower thorax aperture so as to obtain additional information about the direction of the movement of the blood within the thorax from the resulting change in the impedance curve To gain information about the function of the left and right heart. As is known, the heart pumps the blood to the lower left into the aorta lying to the left of the heart, so that the largest vector of the blood goes down to the left, this vector can with the optional removal of one of the lower thorax aperture electrode elements 81, 82, 81 ', 82 'be better recognized.

The actual arrangement and characteristics of the electrode elements as double or triple electrode elements will depend on the corresponding requirements. It will be attempted to extract the maximum amount of information with a minimum of electrode elements. The minimum of electrodes is particularly important in intensive care units, where eventually with a two-electrode element on the neck 80 'and one or two triple-electrode elements on the trunk 81, the gag must be found. Another very economical variant, but with a maximum of information results from a Zweifachelektrodenelement 80 'at the neck, two further electrode elements 81', 82 'left and right at the lower thorax aperture, and a single Zweifachelektrodenelement 85 on one side at the lower end of the Rumofes and one at the corresponding lower end of the same lower limb 7. This variant, which contains only five Zweifachelektrodenelemente that could also be handled for intensive care units, not only extremely accurate cardiac output, but also in addition the Flüssigkeitsvertielung in the body divided into extracellular space and intracellular space and also the fluid displacement from one half of the body to the other is detected. A feed of the current is uniformly effected by the electrode element 80 'at the upper end of the trunk and the electrode element 7 at the lower extremity. The electrodes of the electrode elements 80 ', 7 lying in the direction of the center of the body and the respective two electrodes of the electrode elements 81', 82 'and of the element 85 are connected exclusively as voltage electrodes.

In addition, the serum sodium could also be included in the calculation of the liquid volumes. As is well known, this is the main ion in the extracellular space and thus makes up mainly the conductivity and the impedance. Now it comes in heart disease, for which the method and device according to the invention is also designed, often to a significant drop in serum sodium from a standard value of 140 mmol / liter up to 115 mmol / liter, so that the ionicity and thus the conductivity can fall by 20%. If necessary, this would have to be done by entering the serum sodium or the ionicity into the equations used be taken into account. On the other hand, the hematocrit also influences the conductivity of the blood; if this is approximately constant, as is usually the case, a change in the serum sodium can also be detected with the changes in the impedance measured during cardiac action at several frequencies.

An important application of the method may also be to calculate indirect hormone concentrations in the blood in addition to the output of stroke volume, ejection fraction, diastolic function, lung wedge pressure, total body water, extracellular space and fluid displacement. For example, the concentrations of natriuretic peptide, e.g. Brain Natriuretic Peptide, or Propeptide, atrial natriuretic peptide and also called ADH. The Natriuretic Peptides are currently used in clinical routine for the screening and diagnosis of heart failure. The determination requires a blood sample and is very expensive (currently about 40 euros). With a typical number of about 20 heart patients / day in an outpatient department, one can calculate how quickly a single device according to the invention would have paid for itself. The regulation of these hormones is closely related to the fluid balance and stretching of the heart by these fluids. With detailed knowledge of the household of the fluids and their displacement by the heart action, it is therefore possible to predict the concentration of these hormones in the blood and thus save the expensive blood determination. The determination of all these parameters from the method according to the invention is carried out, for example, in empirically by measuring the parameters with the gold standard methods, in the case of the hormones by the blood determination in a representative number of patients and estimating the parameters of interest with the measured electrical parameters, e.g. using multiple regression equations or using neural networks, other machine learning algorithms or any other black box model.

From the US patent US 5 335 667 A Kichul Cha, the electrode assembly according to the invention differs quite significantly: In this document is Although the body is divided into segments for the measurement of the body composition, the essentially same segment can never be examined with different lengths and therefore no electrically operative length can be calculated. For this reason, yes in the US 5 335 667 A continue to be carried out as a crutch, the circumferential measurement and the manual length measurement of the examined segment. This is done with the centimeter measure and a caliper such as in Fig. 5 from US 5 335 667 A shown.

In the present application, however, it is shown that the measured on the surface length of the segment has nothing or little to do with the calculated "electrically operative length" has, as from Figure 3 evident. And that is the very essential advantage of the method according to the invention. As in Fig. 9 and Fig. 10 Despite the enormous significance of the method according to the invention, the number of electrodes is absolutely practicable, above all since they are all designed as multiple electrodes. In the Fig. 10 The electrode arrangement shown also has the great advantage that changes in position along the longitudinal axis of the body can now be detected automatically for the first time, since any change in position of the body along the longitudinal axis results in significant fluid displacements. These fluid shifts affect the venous return to the heart and thus the cardiac output, and also causes a venous insufficiency when erecting the body along the longitudinal axis significantly larger fluid shifts, so that a venous insufficiency can be well recognized. Especially in combination with a protractor can then be decided whether the fluid displacement is adequate or inadequate for the predetermined change in position and also whether the measured cardiac output change is adequate for the measured fluid displacement.

These examinations can be performed excellently on the tilting table, for example. The electronic effort is minimal, because measuring at several frequencies and switching from one electrode to the other so no expensive or complicated equipment parts needed. This makes also conceivable, this procedure also for the To provide home care of the patient by providing him such a device to the patient for the home. For this purpose, the simultaneous co-detection of the ECG course, particularly favorable. The position of the electrodes on the body, as in Fig. 9 and 10 shown is also excellent for the derivation of the ECG. This could also provide the patient with his own cheap reusable electrodes. These electrodes could, for example, be made of conductive material with stretchable bands, as well-proven by the pulse measuring devices known in sports practice. In the example deformable bands, for example made of non-conductive material, the conductive material, such as band-shaped or eg as a spot, for example in the form of conductive rubber, incorporated, which are then attached by means of stretchable, openable, circular band on the body. These electrodes can then also be easily applied by the patient, relatives or nursing staff.

These results would not then have to be calculated completely or not completely in the patient home device, but could also be used, for example. by radio or by leased line, e.g. by telephone or email, to a central office, where the results are finally evaluated.

This development, known as "telemedicine", is particularly relevant for cardiac patients who currently require close monitoring in expensive specialist outpatient clinics. Heart patients are often transported to the expensive facilities on a monthly basis and often with rescue services in order to optimize therapy. These heart patients often have an equally bad or worse prognosis than cancer patients and the therapy must be constantly adapted to keep them alive. In addition, in the aging of the patients heart disease and especially heart failure increase enormously and have already become a public epidemic in the industrialized countries. In the detected by the method and apparatus of the invention and possibly transmitted via telemedicine a center changes, eg deterioration of cardiac output, overhydration, etc. can then either the Transport to the center in time, or by phone or by email, the therapy can be optimized, or be saved at a good function of the circulation control at a center. Thus, large savings in money are secured despite the use of new technology. When sending the raw data or only rough preprocessed data in the patient device so local Intellegenz saved in the measuring device 12 and so the device can be made even more cost effective.

From impedance tomography, the method and device according to the invention can be well defined, as seen in impedance tomography in each case numerous electrodes at the same height in the longitudinal direction of the body, so from the located in the same sectional plane impedances an image of the liquid distribution in this plane and to calculate a three-dimensional liquid distribution from numerous levels. Our method, on the other hand, does not aim to reconstruct a plane, or reconstruct the fluid distributions in space, but to measure the fluid displacement along the longitudinal axis, taking into account for the first time the electrically operative distance.

Fig. 11 shows an example embodiment of a multi-Spotelektrode 14, wherein the constant electrode spacing can thereby be ensured that the connecting cable between the electrodes is maximally stretched between the electrodes at the time of application to the body, and that by the attachment of the electrodes, a change in the electrode spacing preferably is accomplished in the longitudinal axis of the body. To ensure that the electrode spacing is actually maintained by the user, a relatively stiff spacer 16 may also be present between the electrodes, whereby the connecting cable may also be made rigid as an electrode spacer 16, thereby ensuring that the distance is maintained. When calculating an operative difference d _o , the electrodes can be glued to each other at any distance and a spacer is unnecessary.
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Claims (50)

1. A method for measuring the volume, the composition and the movement of electroconductive body fluids, based on the electrical impedance of the body or a body segment, in particular for performing electromechanocardiography (ELMEC) or impedance cardiography (IKG) measurements for determining hemodynamic parameters, wherein an alternating measuring current of at least one frequency is introduced into the body by means of measuring electrodes attached to the body surface, characterized in that the impedance and temporal variations thereof of essentially the same body segment through which the alternating measuring current flows are measured for at least two different measuring lengths (L, L2, L3, L4, L5), essentially in the longitudinal direction of the body.
2. The method according to claim 1, characterized in that the impedance is sensed at the thorax close to the inferior and superior thoracic apertures for at least two different measuring lengths (L, L2, L3, L4, L5) of essentially the same body segment.
3. The method according to the claims 1 and 2, characterized in that the electrical current is introduced at or close to the upper body end, such as at the neck, the head, the arms, and the lower body end, such as at a leg or at both legs, and that the impedance is measured at the thorax and/or trunk for at least two different measuring lengths (L, L2, L3, L4, L5).
4. The method according to any one of claims 1 to 3, characterized in that the impedance of at least one lower extremity is sensed for at least two different measuring lengths (L, L2, L3, L4, L5) of essentially the same body segment.
5. A method for either performing conventional impedance cardiography measurements or according to any one of claims 1 to 4, characterized in that additionally the whole-body impedance between the lower und upper body ends is measured.
6. The method according to any one of claims 1 to 5, characterized in that the length difference (d, 1, a, a1) between the two different measuring lengths is small compared to the length of the examined body part.
7. The method according to claim 6, characterized in that the ratio of the length of the examined body part to the length difference (d, d1, a, a1) lies between 3:1 and 30:1.
8. The method according to claim 7, characterized in that the ratio of the length of the examined body part to the length difference (d, d1, a, a1) is approximately 10:1.
9. The method according to any one of claims 1 to 8, characterized in that on the basis of the impedance values determined for the different measuring lengths (L, L2, L3, L4, L5) between electrodes an operational electrode measuring length (L₀), which corresponds to the electrically operational length of the body segment, and optionally an operational electrode distance (d₀) are calculated.
10. The method according to claim 9, characterized in that the electrically operational length of the body segment is calculated according to the formula L₀ = d/(Z₀₂/Z₀₁ - 1), wherein d is the difference between the two electrode measuring lengths used for the measurement, Z₀₂ is the impedance for the longer electrode measuring length, and Z₀₁ is the impedance for the shorter electrode measuring length.
11. The method according to any one of claims 2, 3, 5, and 6 to 10, characterized in that the voltage electrodes at the inferior thoracic aperture are provided as double electrodes (81, 82, 81', 82') on the left and right side, respectively, of the thorax, wherein the electrodes positioned at the same distance in the longitudinal direction are electrically connected to each other.
12. The method according to claim 11, characterized in that the electrodes (81, 82, 81', 82') on the left and right side, respectively, of the thoracic aperture may selectively be switched off.
13. The method according to claim 3, characterized in that the voltage electrodes (85, 85', 85") at the lower end of the trunk are provided as double electrodes on the left and right side, respectively, of the lower end of the trunk, wherein the electrodes positioned at the same distance in the longitudinal direction are electrically connected to each other.
14. The method according to claim 13, characterized in that the electrodes on the left and right side, respectively, of the lower end of the trunk may selectively be switched off.
15. The method according to any one of claims 1 to 14, characterized in that the impedance variations with respect to time are measured at at least two frequencies.
16. The method according to claim 15, characterized in that the impedance is measured at three different frequencies.
17. The method according to claim 16, characterized in that the different frequencies amount to between 1 and 10 kHz, approximately 30 to 100 kHz and above approximately 200 kHz.
18. The method according to any one of the preceding claims, characterized in that the maximum temporal variation of the measured impedance values (dZ/dt) is determined at at least two different measuring frequencies, and that the resistivity of the blood present in the body is determined therefrom.
19. The method according to claim 18, characterized in that the maximum temporal variation of the measured impedance value, especially in relatively narrow time frames, is determined at different times of the cardiac cycle.
20. The method according to claim 19, characterized in that the time frames are set at an abrupt rise of resistivity and at the time of minimum blood flow at the end of a diastole.
21. The method according to the claims 19 and 20, characterized in that the time frames are cover the whole cardiac cycle in the form of narrow gliding frames.
22. The method according to any one of claims 15 to 21, characterized in that the frequency of the alternating measuring current is continuously varied from a lower measuring frequency to a higher measuring frequency.
23. The method according to claim 22, characterized in that the lower measuring frequency amounts to approximately 1 kHz and the higher measuring frequency to a maximum of approximately 1000 kHz.
24. The method according to any one of claims 15 to 23, characterized in that the measuring current is impressed for at least one other current electrode distance and at several different measuring frequencies, and that the impedance is measured for the different voltage measuring lengths and at the different frequencies.
25. The method according to any one of claims 1 to 24, characterized in that the phase angle between the measuring current and the measuring voltage is determined.
26. The method according to any one of claims 1 to 25, characterized in that amplitudes, areas and ascending or descending tangents of the impedance waves B, C, X and O are used independently or together for calculating hemodynamic parameters.
27. The method according to any one of the preceding claims, characterized in that empirical equations that have been determined by means of a gold standard, for example by means of the Fick principle for stroke volume, or, for example, echocardiography or isotope methods for other parameters, such as ejection fraction, pulmonary wedge pressure, diastolic function and the like, are used for measuring hemodynamic parameters.
28. The method according to any one of claims 1 to 27, characterized in that the sodium content in serum is determined and used in the calculation of relevant parameters.
29. The method according to any one of claims 1 to 28, characterized in that the sodium concentration in serum is mathematically estimated by the method according to any one of claims 1 to 27 and obtained as a result thereof.
30. The method according to any one of claims 1 to 29, characterized in that the hormones, such as ADH and natriuretic peptide, especially brain natriuretic peptides and precursors thereof, regulating the body water as well as its fractions and composition, are estimated by the method according to any one of claims 1 to 29 by means of empirical equations and obtained as a result thereof.
31. The method according to any one of claims 1 to 30, characterized in that the results obtained by means of said method are sent, preferably by telephone or e-mail, in digital form to a central station, where they are further processed and assessed, and that all necessary measures and therapy changes are transmitted to the patient from a remote place.
32. The method according to any one of the preceding claims, characterized in that the body water is determined with its fractions, such as extracellular space and intracellular space, and read out.
33. An apparatus for measuring the electrical impedance or temporal variations thereof in a human body, in particular for performing electromechanocardiography or impedance cardiography (IKG) measurements for determining hemodynamic parameters, for implementing a method according to any one of claims 1 to 32, wherein at least two voltage electrodes (80, 81, 82, 80', 81', 82') are provided, at least one of which is provided as double voltage electrode element, wherein the impedance and the temporal variations thereof may be sensed between said two voltage electrodes.
34. The apparatus according to claim 33, characterized in that said at least one double voltage electrode element is attached to a common insulating carrier sheet (2).
35. The apparatus according to the claims 33 and 34, characterized in that at least one of the voltage electrodes (80) is formed of a triple electrode element consisting of a current electrode (70) and two voltage electrodes (72, 73).
36. The apparatus according to claim 35, characterized in that the current electrode (70) and the double voltage electrode element (72, 73) are attached to a common carrier sheet (2) in the form of a triple electrode element.
37. The apparatus according to any one of claims 33 to 36, characterized in that all the terminals of the electrode elements are brought together in a distribution element (9) by means of connecting leads (10), and that the distribution element is connected to measuring lines and control lines (10a) of a measuring device (12).
38. The apparatus according to claim 37, characterized in that the distribution element (9) can be controlled so that the electrode elements can be connected to different measuring lines and control lines (10a) of the measuring device (12).
39. The apparatus according to any one of claims 33 to 38, characterized in that an angle meter (11) for measuring body inclination is provided.
40. The apparatus according to claim 39, characterized in that the angle meter (11) is positioned on the distribution element (9).
41. A medical electrode element for measuring the electrical impedance or temporal variations thereof in a human body, in particular for performing electromechanocardiography or impedance cardiography (IGK) measurements for determining hemodynamic parameters, by means of a first current electrode (70), which has an electrical terminal for impressing an alternating measuring current, and a first voltage electrode (73, 15), which has a voltage terminal for sensing an electrical measuring voltage, wherein at least one further voltage electrode (71, 72) with a voltage terminal is provided, and wherein the at least one further voltage electrode (71, 72) is positioned at a distance (d, d1) from the first voltage electrode (73, 15), for implementing the method according to any one of claims 1 to 32, wherein the first voltage electrode (73) as well as the at least one further voltage electrode (71, 72) are provided as parallel, electroconductive strips, the widths of the strips being equal to or preferably smaller than the distance between the strips.
42. The medical electrode element according to claim 41, characterized in that the ratio of the length of the strips to the distance between the electrodes (a, a1, d, d1) lies in the range between 2 and 15.
43. The medical electrode element according to the claims 41 and 42, characterized in that the first voltage electrode (73) and the first current electrode (70) as well as the at least one further voltage electrode (71, 72) and/or at least one further current electrode are provided as parallel, electroconductive strips, the widths of the strips being equal to or preferably smaller than the distance between the strips.
44. The medical electrode element according to any one of claims 41 to 43, characterized in that the first voltage electrode (73) and the first current electrode (70) as well as the at least one further voltage electrode (71, 72) are positioned on a common, electrically insulating carrier material (2, 3, 4).
45. The medical electrode element according to any one of claims 41 to 44, characterized in that the carrier material consists of a carrier sheet (2), and that the first voltage electrode (73) and the first current electrode (70) as well as the at least one further voltage electrode (72) and/or the at least one further current electrode are attached to one side of the carrier sheet and preferably provided with an electroconductive adhesive layer.
46. The medical electrode element according to any one of claims 41 to 44, characterized in that the carrier material comprises a plurality of sheet strips (3) with adhesive surfaces, to which the first voltage electrode (73) and the first current electrode (70) as well as the at least one further voltage electrode (72) are attached, and that the sheet strips (3) with the electrodes (70, 72, 73) secured thereon adhere to a common base carrier sheet (4) in a substantially parallel arrangement, wherein said base carrier sheet (4) may be peeled off from the sheet strips (3) after they have been attached to the body surface.
47. The medical electrode element according to any one of claims 41 to 46, characterized in that the carrier sheet (2, 4) at one longitudinal end is tapered to form a plug-type surface (6), on which the first voltage electrode (73) and the first current electrode (70) as well as the at least one further voltage electrode (72) and/or the at least one further current electrode are provided in a closely spaced way.
48. The medical electrode element according to any one of claims 33 to 40, characterized in that the first voltage electrode and the first current electrode as well as the at least one further voltage electrode and/or the at least on further current electrode are provided in the form of spot electrodes (14), which are spaced from each other by means of spacers (16, 17), such as by a common carrier sheet (85").
49. The medical electrode element according to any one of claims 33 to 40 as well as any one of the claims 41 to 43 as well as claim 48, characterized in that the electrode elements consist of reusable, at least partially flexible and/or elastic, electrically nonconductive or poorly conductive, circular, openable bands, into which the conductive material of the electrodes is incorporated, e.g. in the form of strips or spots.
50. The apparatus according to any one of claims 33 to 49, characterised in that the electrodes or electrode elements are also operated as ECG electrodes.

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